Modern telecommunication systems include facilities to permit use of telecommunication systems by those who are deaf or hard of hearing. The best known form of such communication makes use of devices known as telecommunication devices for the deaf (TDD), also known as text telephones (TTY). TTY communication is widely used between deaf people. Hearing users communicate with deaf users who are users of TDD devices through so-called “relays.” A relay is a telecommunication intermediary service, funded by telephone communication surcharges, which is intended to permit deaf or hard of hearing people to utilize the normal telephone network. At a relay, an operator referred to as a call assistant intermediates between a deaf user and a hearing person by communicating with the deaf person using a TDD and communicating with the hearing person by voice over a normal telephone line.
Previous technology has enabled the relay system to be used to provide a form of enhanced telephone communication for people who are not deaf, but are hard of hearing. This approach to telecommunications is exemplified by U.S. Pat. Nos. 6,307,921 and 6,075,842, the disclosure of which is incorporated by reference. These patents, entitled “Text Enhanced Telephony,” referred to a system that provides captioned telephone service, a service currently marketed under the service mark Captel by Ultratec, Inc. and its licensees. A captioned telephone, or telephone enabled to do text enhanced telephony, is capable of providing a text message to a user of the words which are transmitted to that user over a conventional telephone line. The captioned telephone user receives normal voice from the party on the other end of the line, as well as a text transcription of the words spoken by the other party, so that the user may refer to the text for missed words in the conversation. This capability is made possible by automation in the relay which permits text or captioning to be delivered nearly simultaneously with voice. In addition, the telephone station of the assisted user is specially configured to facilitate the set up of captioned telephone calls.
In its original conception, the text assisted telephone system was designed to be deliverable to and operated by a user over a single telephone line to the user. As the costs of telephone service drops, it is now apparent that many users of captioned telephone service may elect to use two telephone lines to take full advantage of the opportunity for improved service that comes from text enhanced telephone. The concept of using two telephone lines to provide captioned telephone service in general to an assisted user is disclosed in U.S. Pat. No. 6,603,835, the disclosure of which is incorporated herein by reference.